The subject matter of the present invention is a method for the preparation of 2-chloroethyldichlorosilanes by the reaction of vinyldichlorosilanes with hydrogen chloride in the presence of anhydrous metal chlorides.
German Auslegeschrift No. 22 39 412 discloses a method for reacting vinylmethyldichlorosilane with hydrogen chloride in the presence of anhydrous aluminum chloride to form 2-chloroethylmethyldichlorosilane. The reaction temperature, however, must be below 0.degree. C., and the separation of the desired chloroethylmethyldichlorosilane by distillation from the byproducts and the aluminum chloride can be performed only with intense cooling of the produce receivers, because otherwise, at temperatures from 10.degree. to 20.degree. C., the chloroethyldichlorosilane degrades again with the formation of the starting products or of methyltrichlorosilane and ethylene.
To remedy these disadvantages, a method is described in German Offenlegungsschrift DE-OS No. 24 58 962 according to which the distillation is performed in the presence of alkali chlorides. If these measures are taken, the distillation can be performed up to bottom temperatures of 90.degree. C. at pressures between 15 and 30 mbar; nevertheless, yields of a maximum of 71% are obtained, which thus are inadequate for technical purposes.
Furthermore, a method is known from German Offlegungsschrift DE-OS No. 31 44 020 for performing the reaction of the vinyldichlorosilane with hydrogen chloride in the presence of alkyl aluminum compounds, and performing the subsequent distillation in the presence of siloxanes. A disadvantage of this process is the circumstance that the hydrogen chloride addition must be performed at temperatures below 0.degree. C. in order to limit the formation of methyl trichlorosilane and ethylene. In spite of the addition of siloxane, yields of only around 85% are obtained in the final distillation.
The problem therefore existed of conducting the reaction of vinyldichlorosilanes with hydrogen chloride to form chloroethyldichlorosilanes such that it will be possible to operate at room temperature of slightly elevated temperatures, that, in the reaction and subsequent distillation, the formation of byproducts such as methyl- or ethyltrichlorosilane or the re-formation of vinyldichlorosilanes will be largely prevented, and yields of more than 90% will be obtained.